This invention relates to solar concentrators, specifically paraboloid dish reflectors used for concentrating solar energy onto nearby receivers.
The Greenhouse Effect is a problem that can only be solved with cost effective solar energy systems. Solar collectors in remote areas in the countryside can collect summer solar energy and supply city winter base and peak heat and hot water demands by utilizing district heat distribution with seasonal heat storage. Communities in Northern Europe are 100% solar heated with hot water in the winter using district heating systems powered by solar collectors that operate only in the summer.
Reflecting solar concentrators are the most efficient solar heat collectors. The cost of materials compared with the energy delivered indicates that solar concentrator technology should be exceedingly cost effective. There are thousands of solar concentrator designs and scores of prototypes. However, the manufacture of solar concentrators does not exist. Complexity of implementation is a prior-art problem. Lack of information, materials, and manufacturing skills create impediments for market introduction and rapid expansion of cost effective solar concentrators.
Prior-art mirrors used in solar concentrators are commonly made from flat glass coated with silver, followed by moisture protection layers made from copper films, paint, sheet metal, or a second layer of flat glass or glass like substance. Silvered low-iron glass mirrors are 96% efficient. Painted glass mirrors have long-term outdoor lifetimes. The prior art also demonstrates soft mirror materials such as flexible reflecting polymer films, polished metals, and acrylic refractors. These soft materials were used for making curved solar reflectors because glass was considered hard, rigid, and brittle, and therefore would not bend sufficiently for nearby dish receivers. However, the soft materials failed in the field due to low efficiency, short-term lifetimes, poor specular reflection, ultraviolet degradation, and excessive dirt buildup. U.S. Pat. No. 4,372,772 describes a system bending flat glass mirrors in a solar dish concentrator which results in glass being bent to an extent previously thought not possible. However, this glass is only bent and does not form parabolic curves, therefore does not form the high-intensity uniform flux required by high-intensity photovoltaic cells.
There are three generic types of solar mirror concentrators; heliostats or central receiver type, parabola troughs or line focus type, and paraboloid dishes or point focus type. Heliostats are substantially flat reflectors concentrating sunlight onto distant towers. The disadvantages of heliostats include critical mirror contour requirements and the expense of tall towers supporting remote receivers. Troughs are simple-curve parabolic reflectors concentrating sunlight onto long receiver pipes spanning the full length of the reflectors. The disadvantages of troughs include low maximum solar concentration, high receiver heat loss, and high receiver cost. Both heliostats and troughs do not face directly at the sun therefore both have reduced performances known as cosine losses. Solar dishes are compound-curve paraboloidal reflectors concentrating sunlight onto small receivers supported near the centers of dish apertures. Dishes achieve the highest solar concentrations, the best efficiencies, and face directly at the sun. The disadvantages of dishes includes the cost of compound and complex reflector curves and expensive mirror substrates. Both heliostats and dishes require accurate optical mirror contours and accurate optical dual axis tracking. These optical accuracy requirements have been significant cost barriers in the prior art.
Prior-art solar dish concentrator methods and designs also have disadvantages from unnecessary construction complexity. These include forming compound and complex structural curves, molding substrates for controlling mirror curve contours, deflecting reflective membranes with air pressure, heat sagging glass for making fixed curved mirrors, structures with contiguous mirror support for mirror curve shaping, systems for avoiding mirror thermal stress from dissimilar structural materials, curving mandrels, reflected laser light for mirror adjustments during construction, expensive motorized solar tracking drives, tracking rails, and pivot bearings. Performance disadvantages of the prior art include shade from receiver supports and non-uniform flux on high-intensity photovoltaic cells at the focus.
The advantages of the present invention resolves one or more prior-art solar dish disadvantages with the simple use of readily available materials manufactured in high volume from existing large industries. These materials are flexed into accurate parabolic curves with existing skills and without special tools nor measurements. Curved parts and curved templates are not used for construction. Substrates are not used. Rather, spans of straight struts are parabolically curved and spans of flat glass mirrors are parabolically curved during construction from deflection of rigid materials stressed with lateral forces. The lateral forces are applied by a method of assembling the rigid materials into flexed solar dish concentrators. The stressed parabolic materials do not form permanent curves and would spring flat again if disassembled, thereby maintaining force reactions. This parabolic deflection from force reactions demonstrates a natural phenomenon that shows parabolic curves are formed from opposing forces, such as the curves of wires between poles, the trajectory of canon balls, and the deflection of horizontal structural beams from gravity. The disclosed invention uses this phenomenon to make accurate parabolic curves from flat raw materials flexed during assembly of solar dish concentrators in the field.
All of the parts are the same size and are identical for easy assembly. This unity occurs when the mirror supporting framework is assembled perpendicular or normal to the dish aperture rather than, as the prior art shows, assembled perpendicular or normal to the reflecting surfaces. Trusses supporting paraboloid glass mirrors at specific angles less than normal permit accurate parabolic trusses with equal focal lengths to accurately support paraboloid glass with varying focal lengths required by paraboloidal shapes and solar dish optics. The dish has a rectangular aperture to support uniform rectangular glass for easy assembly and low waste manufacturing.
The flexed glass mirror solar dish concentrator is optically accurate and delivers uniform high-intensity solar flux greater than 1000 suns. Mirror shaping substrates are not necessary. Post construction adjustments are not necessary. The solar dish concentrators can be constructed worldwide with indigenous skills and with off-the-shelf materials at costs well below the current costs for fossil fuels. High volume solar dish manufacturing firms are not required for low cost implementation. Special manufacturing tools are not required.
Thus, it is a general object of the present invention to provide a paraboloidal glass mirror and a altazimuth solar tracking mirror support framework which overcomes one or more of the disadvantages of the prior art noted above. Other objects and advantages will become apparent from the specifications and drawings.
It is a further object of the present invention to supply vast amounts of solar energy at costs substantially less than the costs of fossil fuels, solar energy supplied from millions of light-weight durable solar dishes assembled indigenously with heavy application of available raw materials from large existing industries.
It is a further object of the present invention to provide a paraboloidal dish reflector apparatus which has a geometry particularly suitable for quick assembly from identical parts without special tools or skills.
It is a further object of the present invention to provide a method for making accurate smooth paraboloidal space frames from flexed linear members without curve measurements and adjustments.
It is a further object of the present invention to provide a system and a method for flexing flat glass mirrors to form accurate parabolic curves without curve measurements and mirror alignments.
It is a further object of the present invention to provide accurate glass mirror solar dishes made without mirror support substrates.
It is a further object of the present invention to provide parabolic dishes suitable for reflecting uniform high-intensity solar flux onto concentrator photovoltaic cells.
It is a further object of the present invention to provide a system for supporting dish receivers configured for minimum receiver shading.
It is a further object of the present invention to provide a system for accurately tracking solar concentrators towards the sun with off-the-shelf weather resistant components mass produced for other products.
Accordingly, the present invention is a parabolic solar dish which includes a rigid support matrix of substantially paraboloid configuration, which comprises a plurality of strut-like members which are in turn joined together forming trusses substantially within planes parallel to the axis of symmetry of a paraboloid, planes that do not intersect the axis of symmetry of the paraboloid. The concave parabolic edges of the trusses are produced by patterns of intersections of the paraboloid and the aforementioned planes. This method of pattern definition is used to create uniform trusses and uniform strut-like members throughout a paraboloid space frame. The method of connecting the strut-like members flexes rigid linear truss rails into identical smooth parabolic curves.
The present invention also includes a system for flexing otherwise rigid flat glass mirrors which have a rectangular and slender shape. The system includes a space frame for supporting the slender flat glass mirrors near each mirror corner and button tension elements positioned at predetermined points along the long edges of the slender flat glass mirrors for applying forces normal to the reflecting surfaces. The force flexes spans of the rigid slender flat glass mirrors into substantially accurate parabolic curves suitable for high-intensity uniform flux solar applications, such as illuminating high-intensity photovoltaic cells. The mirror curve becomes hyperbolic near the mirror corners and sunlight reflected from these regions will not be intercepted by high-intensity photovoltaic cells.
The present invention also includes a system for altazimuth tracking the angle of the sun. The system includes an azimuth drive support apparatus that adapts to not level ground for rotating the solar dish concentrator utilizing a drive wheel, such as a bicycle wheel, in contact with the ground and a second wheel driving the rim of the drive wheel for speed reduction. A small gear motor drives the rim of the second wheel. A zenith tracking drive is made with a television satellite dish actuator or screw-jack drive. Solar tracking becomes accurate with small low-cost drive motors and solid state microprocessors. Reliability is enhanced with weather resistant components such as bicycle wheels and dish actuators.
The present invention also includes a system for supporting a solar dish receiver at the apex of a cone of reflected sunlight. The system includes two energy transport support tubes outside the cone of reflected sunlight and two guy wires outside the cone of reflected sunlight for supporting the receiver with minimum loss from direct shade and reflected shade.